Displaying a wideband spectrum using a narrowband receiver

ABSTRACT

Methods of aggregating spectrum data captured from a narrowband radio to form a spectrum covering a much wider frequency band. Frequency data, such as FFT spectrum data captured from a narrowband receiver such as an IEEE 802.11 Wi-Fi receiver are combined to display representative real-time FFT, average FFT, and FFT duty cycle data of a wideband spectrum. Data is captured from narrow band radios such as access points, station monitors, or client devices on a wireless network. A wideband spectrum may be aggregated from data captured from one or from multiple devices. Data may be stored for later analysis and display.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of priority on U.S. ProvisionalPatent Application No. 61/321,210 filed Apr. 6, 2010 and entitled“Automatic conversion of access points to spectrum monitors and hybridmode access point”, U.S. Provisional Patent Application No. 61/321,179filed Apr. 6, 2010 and entitled “Measuring and displaying wirelessnetwork quality”, and U.S. Provisional Patent Application No. 61/321,214filed Apr. 6, 2010 and entitled “Displaying a Wideband spectrum using anarrowband receiver”, all incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to wireless digital networks, and inparticular, to combining data from narrowband receivers to displayrepresentative wideband spectra.

Wireless digital networks are becoming ubiquitous in enterprises,providing secure and cost-effective access to resources. Those networksusually have a plurality of access points (AP) deployed through theenterprise. WiFi networks operating in accordance with IEEE 802.11standards are examples of such networks.

Unfortunately, the frequencies used by these networks are shared. Theyare shared not only among the wireless networks themselves, but alsowith other non-network radiators. Non-network radiators, devices such asmicrowave ovens, wireless video streaming devices, cordless phones andthe like, as well as other wireless networking devices, can causeinterference with the operation of a network. Interfering devices cancome and go, change their nature, and move around. As an example,replacing or adding a microwave oven in an employee lounge area candramatically alter the interference present to a network.

In searching out sources of interference to a wireless network, variouspieces of test equipment such as spectrum analyzers are used. Aprofessional spectrum analyzer has a calibrated receiver of exquisitesensitivity, and is able to display and measure signals over a widerange of frequencies and amplitudes. They also range in price from a fewthousand dollars to tens of thousands of dollars, and require a skilledoperator. This places them outside the realm of the normal wirelessnetwork engineer.

What a digital wireless network does have is a plurality of narrowbandradios, in the form of access points and wireless client devices. Whilethese radios may not have the performance of a high quality spectrumanalyzer, they are capable of collecting data on narrow portions of thespectrum used by the network.

What is needed are tools to combine narrowband spectrum information todisplay representative wideband spectra.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by referring to the followingdescription and accompanying drawings that are used to illustrateembodiments of the invention in which:

FIG. 1 shows devices in a wireless network.

DETAILED DESCRIPTION

Embodiments of the invention relate to methods of aggregating spectrumdata captured from a narrowband radio to form a spectrum covering a muchwider frequency band. Spectrum data such as Fast Fourier Transform (FFT)data captured from a narrowband receiver such as an IEEE 802.11 Wi-Fireceiver, are combined to display representative real-time FFT, averageFFT, and FFT duty cycle data of a wideband spectrum.

Spectrum data is captured by a narrowband radio operating on aparticular channel with a given frequency and channel width. Such datafrom multiple channel scans, overlapping or nonoverlapping, are combinedto form a representative spectrum covering a much wider frequency band.

FIG. 1 shows a network in which controller 100 communicates with adigital network such as the Internet 150. Controller 100 also supportsdevices such as access points (AP) 200 and spectrum monitors (SM) 300.Wireless client devices 400 connect to APs 200 and access services suchas the Internet 150 through controller 100.

Also shown in FIG. 1 is monitoring process 180 and display 190. Whileshown as a separate device communicating with controller 100, monitoringprocess 180 may operate within controller 100, or on any suitablecomputing device attached to the network, such as a laptop or desktopcomputer.

As is known to the art, controller 100, APs 200, and spectrum monitor300 are purpose-made digital devices, each containing a processor,memory hierarchy, and input-output interfaces. In one embodiment of theinvention, a MIPS-class processor such as those from Cavium or RMI isused. Other suitable processors, such as those from Intel or AMD mayalso be used. The memory hierarchy traditionally comprises fastread/write memory for holding processor data and instructions whileoperating, and nonvolatile memory such as EEPROM and/or Flash forstoring files and system startup information. Wired interfaces aretypically IEEE 802.3 Ethernet interfaces, used for wired connections toother network devices such as switches, or to a controller. Wirelessinterfaces may be WiMAX, 3G, 4G, and/or IEEE 802.11 wireless interfaces.In one embodiment of the invention, controllers and APs operate undercontrol of a LINUX operating system, with purpose-built programsproviding host controller and access point functionality.

Wireless client devices 400 contain a processor, memory hierarchy, and anumber of interfaces including a wireless interface for communicatingwith APs 200. Typical wireless client devices include personalcomputers, handheld and tablet computers, Wi-Fi phones, wireless barcodescanners, and the like.

Traditional spectrum analyzers use wideband receivers so that they canmonitor the entire frequency spectrum of interest at all times. Theadvantage of wideband receivers is that data can be collected andprocessed in real-time for an entire band to support the display ofreal-time FFT, FFT average, and FFT duty cycle. Traditional spectrumanalyzers typically use purpose built hardware with specialized spectrumanalysis software and are made by companies such as AgilentTechnologies, Rhode & Schwarz, and Anritsu.

According to the present invention, methods are provided for supportingspectrum analysis functions using data collected from a narrowband radiosuch as an IEEE 802.11 radio. The radio may or may not be providingservices to IEEE 802.11 clients while acting as a spectrum analyzer.Suitable radios include the radios in network access points and inwireless client devices where such data collection is supported by thedrivers operating the radio. An IEEE 802.11 radio is only capable ofreceiving signals that fall within 5 to 40 MHz wide channels, since IEEE802.11 channels are either 20 MHz or 40 MHz wide. Future IEEE 802.11radios may be able to operate in 80 MHz channels. The width of thechannel in an 802.11 radio receiver is restricted to the channel widthsdefined by the IEEE. There may also be other constraints such as therequirement to receive 802.11 frames, provide intrusion detectionsystems (IDS), and support interference classification that may limitthe channel widths and dwell times that can be used by an 802.11 radio.The methods described here apply to any narrowband receiver such as thatimplementing IEEE 802.11, IEEE 802.16 or IEEE 802.15 standards orsimilar protocols that can be used to construct a standalone spectrumanalyzer or a spectrum analyzer that provides spectrum analysisfunctions along with any combination of client connectivity services(e.g., as an Access Pont), Interference Classification, or IDS.

For spectrum analysis, the spectrum of interest at any time could be aswide as 200 MHz or more. In order to support such wideband spectrumvisibility using a narrowband radio, the spectrum analyzer (radio) needsto “scan” multiple channels in real-time and combine the time andfrequency domain information gathered from multiple channels to form acoherent view of the wideband spectrum. The spectrum analysis functionselects the best set of FFT samples among the hundreds or thousands ofavailable samples per second that accurately represents the view of thespectrum in order to display the entire spectrum on a device such as acomputer display.

An FFT sample from a narrowband radio is represented as a set ofamplitude values where each amplitude value corresponds to a frequencybin. The number of frequency bins in an FFT sample is determined by thechannel width and the FFT size. For example, an FFT on a 20 MHz channelmay produce FFT samples with 64 frequency bins, with each binrepresenting 312.5 KHz (i.e., 20 MHz/64). Other parameters associatedwith FFT include the starting frequency, the sampling time, and thesampling frequency or interval. The sampling time is the amount of timespent taking one FFT sample and the sampling frequency is the number ofsamples per second.

For each display interval, the dwell time, which is the amount of timeto be spent looking for activity on each channel is selected. The dwelltime on each channel may be fixed or may vary based on certainconditions. A fixed dwell time may be obtained by dividing the totaldisplay interval (e.g., one second) by a multiple of the number ofchannels to be scanned. For example, given a display interval of onesecond and the number of channels to be scanned of five, the defaultdwell time would be 200 milliseconds (1000/5) per channel. The defaultdwell time could also be 100 milliseconds (1000/(2×5)), where thespectrum analyzer scans each channel twice within the interval of onesecond. However, a fixed dwell time may not be appropriate under allcircumstances. One such scenario is when the spectrum analyzer alsosupports IDS. A radio supporting IDS and spectrum analysis must be ableto adaptively determine the dwell time on each channel so that IDSfunctions can be effectively supported without affecting the ability toreceive representative FFT information from all channels for an accurateFFT display. The interferer profile is used to determine the amount oftime spent on each channel (dwell time), the sequence of scanning, andthe number of times to visit a channel per display interval. Wheninterferers or rogue devices are detected on a specific 802.11 channel,those channels are scanned with a higher probability. Dwell times arealso accordingly adjusted to capture sufficient 802.11 frames and/or FFTsamples to perform the necessary IDS and interference classificationfunctions.

Some channels are known or likely to have more interferers and/or 802.11devices. For example, microwave ovens operate in a specific frequencyrange in the 2.4 GHz band, and 5 GHz cordless phones operate in aspecific portion of the UNII band. According to the invention, thescanning algorithm assigns a higher weight to those channels to providescanning preference and increased dwell time if necessary.

When a certain type of interferer (e.g. a frequency hopper such as a 2.4GHz frequency hopping phone) is partially detected, the scanningalgorithm adaptively changes the dwell time on a channel to receivesufficient samples on that channel that would help further classify thetype and subtype of the interferer (e.g., Bluetooth, Xbox, cordlessphone).

Another aspect of scanning according to the present invention is toselect among multiple channel widths supported by the radio, including20 MHz and 40 MHz channel scanning. The advantage of 20 MHz scanning isthat all 802.11 devices (including those operating in 20 MHz and 40 MHzchannelization) can be reliably detected. If only 40 MHz channels arescanned, 20 MHz 802.11 devices operating on the extended channel (i.e.,one half of the 40 MHz channel) or 40 MHz 802.11 devices operating withthe different combination of primary and extensions channels cannot bereliably detected.

On the other hand, 40 MHz scanning has fewer channels to scan, and theFFT information obtained from 40 MHz channels is sufficient for theinterference classifier. The process herein disclosed uses a combinationof 20 MHz and 40 MHz scanning to optimize scan efficiency withoutsacrificing the ability to receive and decode 802.11 signals or classifyinterferers. A threshold determines the time interval within which thespectrum analyzer must scan all possible 20 MHz channels within theselected band at least once. The scanning order and dwell time can becombined with this threshold to select the ordering and dwell times ofeach 20 MHz or 40 MHz channel. The same process can be extended to 80MHz channels or higher width channels when available.

Once the dwell time and scanning method are selected, the radio stillcould receive hundreds or thousands of FFT samples and 802.11 frames persecond on each channel. FFT sample selection selects a best sample foreach channel out of thousands and these best samples are combinedtogether to construct the real-time view of the wideband display forevery display interval. The best sample to display is not always thesample with the highest signal strength. The sample selection methodaccording to the present invention uses at least three thresholds toselect the best sample from each channel.

Prior to sample selection, the samples are categorized into Wi-Fi andnon-Wi-Fi samples. The first threshold is used to select the Wi-Fi(802.11) FFT sample with the highest signal strength that exceeds thisthreshold. If no samples exceed the first threshold, no 802.11 sample isselected. The second threshold is used to select the non-Wi-Fi FFTsample with the highest signal strength that exceeds this threshold. Aswith the Wi-Fi FFT samples, if no samples exceed the threshold, nonon-Wi-Fi FFT sample is selected. The third threshold is used to selectthe best of the Wi-Fi and non-Wi-Fi sample for display. The spectrumanalyzer may be configured to prefer non-Wi-Fi samples or Wi-Fi samplesat any time. Alternatively, the system may be configured to provideequal weight to both Wi-Fi and non-Wi-Fi samples. The third threshold,which may be positive or negative or zero, is added to the signalstrength value of the non-Wi-Fi FFT sample. After the third threshold isapplied and the signal strength value is normalized, the sample with thehighest signal strength value is selected for display. The thirdthreshold and therefore the preference for one type of sample over theother may be randomized, if necessary, to accurately portray thespectrum activity on the real channel.

Once the samples are selected per 802.11 channel (e.g., 20 MHz or 40MHz), the samples need to be combined to construct the view of thewideband spectrum. Since the samples selected from adjacent channels maynot be from the same time instance, the FFT display may show FFT binsfrom adjacent channels with significantly different amplitudes. Atechnique of using FFT average information to fill in the FFT bins atthe edge of the channels, as long as the peaks of the FFT do not fall inthese bins, is used to smooth out these differences in amplitude levelsof adjacent channels.

Various methods known to the art may be used to fill in the FFT bins atthe edge of the channels, such as simple averaging among bins. In suchan approach, samples from bins of the same frequency are processedgenerating an average, weighted average, or other similar calculation.As an alternative, a smoothing process may be used incorporating datafrom nearby frequency bins in the process. An example of such a processwould be the application of splines to smooth the transition fromchannel to channel across a range of frequency bins.

When the above described sample selection method is used and a frequencyhopping device is active on the channel it is possible that the sampleselection would always select samples with the highest signal strengthon each channel. Since a frequency hopper hops at a higher rate, it ishighly likely that the radio receives at least one FFT samplecorresponding to a hopper on all channels it scans during a specifiedinterval such as one second. However, this may result in a FFT displaythat incorrectly shows the frequency hopper's FFT signature as aconstant source interferer. Selecting FFT samples in the presence offrequency hoppers uses the knowledge from the classification engine toselect appropriate samples that correctly represents an instantaneousFFT signature. In this case, the FFT sample with the highest signalstrength is not always selected for all channels. Once the identity ofthe frequency hopper is known based on the interferer classification,associated information such as signal strength, occupied bandwidth,hopping rate, hopping pattern, and burst size are known. Sampleselection uses these parameters to select FFT sample signatures thatmatch the frequency hopper's hopping pattern instead of choosing sampleswith highest signal strength on all channels.

Yet another requirement of the FFT display is the ability to see theaverage FFT display over a specified display interval. FFT averagingcombines the converted 802.11 samples and other non-Wi-Fi FFT samples tocalculate the average for every frequency bin. The 802.11 radio isprogrammed to deliver one FFT sample for every FFT_SCAN interval inorder to minimize the impact on the CPU processing. For example, if twoFFT samples are separated by only FFT_SCAN, it can be estimated that thesignal was active for the entire duration of the FFT_SCAN. Therefore,the duration of the non-Wi-Fi interferer signal is accurately estimatedby calculating the time difference between consecutive FFT samples. Theduration of signals is accumulated in units of time that is a multipleof the FFT sampling duration along with aggregated amplitude per bin.The duration of a received Wi-Fi frame is calculated based on themodulation, coding, length and other related parameters. The convertedWi-Fi FFT samples are then used to update the FFT amplitude bins andduration using the same units as the non-Wi-Fi FFT signature. Whenneither Wi-Fi nor non-Wi-Fi signals are present, all FFT bin amplitudesare updated with the amplitude of the noise floor in that instant. Theduration is also updated accordingly. Once every update interval (e.g.,one second), the FFT average amplitude for every bin is calculated bydividing the total amplitude per bin by the total time spent on eachchannel.

Similar to the FFT average, the FFT duty cycle also needs to becalculated for display purposes. The FFT duty cycle indicates thepercentage of time a specific FFT bin has signal amplitude that is abovea specific FFT_DUTY_CYCLE_SIGNAL_THRESHOLD. The duration of the non-FFTsignal above this threshold is accumulated per bin similar to theestimation process described in FFT averaging for each channel. WhenWi-Fi frames are received, the frames are converted into FFT samples andthe FFT duration bins are updated if the corresponding bin in theconverted FFT sample exceeds the FFT_DUTY_CYCLE_SIGNAL_THRESHOLDthreshold. Once every update interval (e.g., one second), the FFT dutycycle for every bin is calculated by dividing the accumulated durationfor each bin by the total time spent on a channel.

According to the invention, spectrum data is collected by one or moreradios on a network, such as access points, dedicated spectrum monitors,or from suitably equipped client devices. Spectrum data may be combinedon a device producing a wideband spectrum, or may be sent in combined oruncombined form to another device such as monitoring process 180 forcombining into a wideband spectrum according to the processes describedherein. As an example, samples from radios are combined by monitoringprocess 180 and displayed on display 190. Samples from physically closeAPs may be combined to provide estimates of the wideband spectrum in aparticular area. These samples may be combined with samples fromsuitable client devices in the area. Such samples may be stored intime-stamped fashion for later combination and analysis.

Monitoring process 180 and display 190 may be present as a separatedevice on the network, or as part of another device such as a wirelessclient in the form of a suitable desktop, laptop, or handheld computer.Sample data from radios such as access points 200 station monitor 300and client device 400 may be stored locally or stored centrally such asin controller 100 for later retrieval and analysis. Such samples may bepushed from a device such as access point 200 to a collection point suchas monitoring process 180, or may be polled or pulled by monitoringprocess 180 working with access point 200.

The present invention may be realized in hardware, software, or acombination of hardware and software. The present invention may berealized in a centralized fashion in one computer system, or in adistributed fashion where different elements are spread across severalinterconnected computer systems. Any kind of computer system or otherapparatus adapted for carrying out the methods described herein issuited. A typical combination of hardware and software may be a generalpurpose computer system with a computer program that, when being loadedand executed, controls the computer system such that it carries out themethods described herein.

The present invention also may be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext means any expression, in any language, code or notation, of aset of instructions intended to cause a system having an informationprocessing capability to perform a particular function either directlyor after either or both of the following: a) conversion to anotherlanguage, code or notation; b) reproduction in a different materialform.

This invention may be embodied in other forms without departing from thespirit or essential attributes thereof. Accordingly, reference should bemade to the following claims, rather than to the foregoingspecification, as indicating the scope of the invention.

I claim:
 1. A non-transitory machine readable medium comprising a set ofinstructions which, when executed by one or more hardware processors,causes performance of a set of operations comprising: accumulatingspectral data from a radio scanning a plurality of channels; for each ofthe plurality of channels, selecting spectral data representing (a) asignal strength of a Wi-Fi signal transmitted on each channel or (b) asignal strength of a non-Wi-Fi signal transmitted on each channel; theselecting operation comprising: for a first channel of the plurality ofchannels: selecting a first spectral data representing a signal strengthof a Wi-Fi signal transmitted on the first channel; for a second channelof the plurality of channels: selecting a second spectral datarepresenting a signal strength of a non-Wi-Fi signal transmitted on thesecond channel; combining the first spectral data re representing thesignal of the Wi-Fi signal transmitted on the first channel and thesecond spectral data representing the signal strength of the non-Wi-Fisignal transmitted on the second channel to produce a spectrum displayrepresenting both: the signal strength of the Wi-Fi signal transmittedon the first channel and the signal strength of the non-Wi-Fi signaltransmitted on the second channel.
 2. The machine readable medium ofclaim 1 wherein the first spectral data representing the signal strengthof the Wi-Fi signal is selected for the first channel based at least onthe signal strength of the Wi-Fi signal exceeding a threshold value. 3.The machine readable medium of claim 1 wherein the first spectral datarepresenting the signal strength of the Wi-Fi signal is selected for thefirst channel based at least on the signal strength of the Wi-Fi signalexceeding a signal strength of a non-Wi-Fi signal transmitted on thefirst channel.
 4. The machine readable medium of claim 1 the firstspectral data representing the signal strength of Wi-Fi signal isselected for the first channel based at least on (a) the signal strengthof the Wi-Fi signal exceeding a signal strength of a non-Wi-Fi signaltransmitted on the first channel and (b) the signal strength of thenon-Wi-Fi signal transmitted on the first channel not meeting athreshold value.
 5. The machine readable medium of claim 1 wherein thesecond spectral data representing the signal strength of the non-Wi-Fisignal is selected for the second channel based at least on the signalstrength of the non-Wi-Fi signal transmitted on the second channelexceeding a signal strength of a Wi-Fi signal transmitted on the secondchannel.
 6. The machine readable medium of claim 1 wherein the secondspectral data representing the strength of the non-Wi-Fi signal isselected for the second channel based at least on the signal strength ofthe non-Wi-Fi signal transmitted on the second channel exceeding athreshold value.
 7. A non-transitory machine readable medium comprisinginstructions which, when executed by one or more hardware processors,causes performance of operations comprising: detecting at least onewireless signal from an interferer device on a first channel of aplurality of channels without detecting any wireless signal from theinterferer device on a second channel of the plurality of channels;responsive to the detecting operation: setting a first dwell time forthe first channel of the plurality of channels: and setting a seconddwell time for the second channel of the plurality of channels that isshorter than the first dwell time for the first channel; scanning thefirst channel for a first period of time, corresponding to the firstdwell time, to generate a first spectral data representing a signalstrength of at least one wireless signal detected on the first channel;and scanning the second channel for a second period of time,corresponding to the second dwell time, to generate a second spectraldata representing a signal strength of at least one wireless signaldetected on the second channel.
 8. The machine readable medium of claim7, wherein the first dwell time and the second dwell time are furtherbased on a device type of the interferer device.
 9. The machine readablemedium of claim 7, wherein the first dwell time and the second dwelltime are further based on a hopping rate of the interferer device forhopping between different channels of the plurality of channels totransmit a plurality of wireless signals.
 10. The machine readablemedium of claim 7, wherein the first dwell time and the second dwelltime are further based on an occupied bandwidth for wireless signalstransmitted by the interferer device.
 11. The machine readable medium ofclaim 7, wherein the first dwell time and the second dwell time arefurther based on a hopping pattern of the interferer device for hoppingbetween different channels of the plurality of channels to transmit aplurality of wireless signals.
 12. The machine readable medium of claim7, wherein the operations further comprise accumulating the firstspectral data and the second spectral data to generate spectrum displayrepresenting one or more wireless signals detected during the firstperiod of time on the first channel and one or more wireless signalsdetected during the second period of time on the second channel.
 13. Themachine readable medium of claim 7, wherein the first dwell time and thesecond dwell time are further based on a frequency band associated withthe first channel and a frequency band associated with the secondchannel.
 14. A system comprising: at least one device including ahardware processor; the system being configured to perform operationscomprising: accumulating spectral data from a radio scanning a pluralityof channels; for each of the plurality of channels, selecting spectraldata representing (a) a signal strength of a Wi-Fi signal transmitted oneach channel or (b) a signal strength of a non-Wi-Fi signal transmittedon each channel; the selecting operation comprising: for a first channelof the plurality of channels: selecting a first spectral datarepresenting a signal strength of a Wi-Fi signal transmitted on thefirst channel; for a second channel of the plurality of channels:selecting a second spectral data representing a signal strength of anon-Wi-Fi signal transmitted on the second channel; combining the firstspectral data representing the signal strength of the Wi-Fi signaltransmitted on the first channel and the second spectral datarepresenting the signal strength of the non-Wi-Fi signal transmitted onthe second channel to produce a spectrum display representing both: thesignal strength of the Wi-Fi signal transmitted on the first channel andthe signal strength of the non-Wi-Fi signal transmitted on the secondchannel.
 15. The system of claim 14, wherein the first spectral datarepresenting the signal strength of the Wi-Fi signal is selected for thefirst channel based at least on the signal strength of the Wi-Fi signalexceeding a threshold value.
 16. The system of claim 14, wherein thefirst spectral data representing the signal strength of the Wi-Fi signalis selected for the first channel based at least on the signal strengthof the Wi-Fi signal exceeding a signal strength of a non-Wi-Fi signaltransmitted on the first channel.
 17. The system of claim 14, the firstspectral data representing the signal strength of the Wi-Fi signal isselected for the first channel based at least on (a) the signal strengthof the Wi-Fi signal exceeding a signal strength of a non-Wi-Fi signaltransmitted on the first channel and (b) the signal strength of thenon-Wi-Fi signal transmitted on the first channel not meeting athreshold value.
 18. The system of claim 14, wherein the second spectraldata representing the signal strength of the non-Wi-Fi signal isselected for the second channel based at least on the signal strength ofthe non-Wi-Fi signal transmitted on the second channel exceeding asignal strength of a Wi-Fi signal transmitted on the second channel. 19.The system of claim 14, wherein the second spectral data representingthe signal strength of the non-Wi-Fi signal is selected for the secondchannel based at least on the signal strength of the non-Wi-Fi signaltransmitted on the second channel exceeding a threshold value.
 20. Asystem comprising: at least one device including a hardware processor;the system being configured to perform operations comprising: detectingat least one wireless signal from an interferer device on a firstchannel of a plurality of channels without detecting any wireless signalfrom the interferer device on a second channel of the plurality ofchannels; responsive to the detecting operation: setting a first dwelltime for the first channel of the plurality of channels; and setting asecond dwell time for the second channel of the plurality of channelsthat is shorter than the first dwell time for the first channel;scanning the first channel for a first period of time, corresponding tothe first dwell time, to generate a first spectral data representing asignal strength of at least one wireless signal detected on the firstchannel; and scanning the second channel for a second period of time,corresponding to the second dwell time, to generate a second spectraldata representing a signal strength of at least one wireless signaldetected on the second channel.
 21. The system of claim 20, wherein thefirst dwell time and the second dwell time are further based on a devicetype of the interferer device.
 22. The system of claim 20, wherein thefirst dwell time and the second dwell time are further based on ahopping rate of the interferer device for hopping between differentchannels of the plurality of channels to transmit a plurality ofwireless signals.
 23. The system of claim 20, wherein the first dwelltime and the second dwell time are further based on an occupiedbandwidth for wireless signals transmitted by the interferer device. 24.The system of claim 20, wherein the first dwell time and the seconddwell time are further based on a hopping pattern of the interfererdevice for hopping between different channels of the plurality ofchannels to transmit a plurality of wireless signals.
 25. The system ofclaim 20, wherein the operations further comprise accumulating the firstspectral data and the second spectral data to generate spectrum displayrepresenting one or more wireless signals detected during the firstperiod of time on the first channel and one or more wireless signalsdetected during the second period of time on the second channel.
 26. Thesystem of claim 20, wherein the first dwell time and the second dwelltime are further based on a frequency band associated with the firstchannel and a frequency band associated with the second channel.